Carbon nanotubes (CNTs) possess unique electrical, optical, thermal and mechanical properties, which make them a promising material for many applications. A problem associated with the use of carbon nanotubes in these applications is that the fabrication and handling of stand alone (free-standing) films comprising carbon nanotubes, or other high aspect ratio molecular (HARM) structures such as carbon nano-buds (a molecule having a fullerene molecule covalently bonded to the side of a carbon nanotube), cellulose fibers, nanowires, nanorods etc., is very challenging with the methods of the prior art. Free-standing films of HARM-structures are needed in various electrical and mechanical device-applications to reduce detrimental effects to the operation of the device caused by a solid substrate over which the film (or network) of HARM-structures resides.
A known method for fabricating free-standing films comprising carbon nanotubes is to vertically grow CNTs as “forests” on a substrate and then to draw a film of these nanotubes from the surface so that individual CNTs contact each other forming a mechanically robust free-standing nanotube sheet called buckypaper. An example of this method is disclosed in scientific publication “Carbon, vol. 45 (2007), pp. 2880-2888”. Another fabrication technique of buckypaper sheets is often referred to as the “domino pushing formation” in which a very thin microporous membrane is placed on top of a CNT array and then a steel cylinder is pushed slowly across the sample. This knocks all the CNTs over in the same direction and flattens them between the membrane and silicon substrate. Next, the membrane and the buckypaper are peeled off the silicon substrate and the membrane is removed, resulting in highly aligned free-standing buckypaper (Nanotechnology 19 (2008) 075609, pp. 1-6).
A drawback of the free-standing buckypaper sheet is that the nanotube molecules are aligned in the sheet, which limits the possibilities to apply the buckypaper material to different electrical devices or to other applications. Furthermore, due to the domino pushing or pulling formation mechanism of the buckypaper, it is challenging to synthesize very thin, very transparent and homogeneous layers of buckypaper with the known synthesis methods. Moreover, fabrication of free-standing buckypaper of single walled CNTs is still a challenging task.